Marine fuel oil, sometimes referred to as bunker fuel, has traditionally provided a use for heavy oil fractions that are otherwise difficult and/or expensive to convert to a beneficial use. Due in part to a relatively high sulfur limit in international waters, vacuum resid fractions as well as other lightly processed (or even unprocessed) fractions can be incorporated into traditional fuel oils.
More recently, many countries have adopted local specifications for sulfur emissions from marine vessels. This can result in some vessels carrying two types of fuel oil, with one type being suitable for international waters while a second type can be used while satisfying the more stringent local regulations. As various local and international specifications continue to become more stringent, the development of additional methods for producing lower sulfur fuel oils and/or marine gas oils will become increasingly important.
U.S. Pat. Nos. 2,425,506, 2,916,446, and 3,529,944 provide early examples of the use of adsorptive clay structures for processing of petroleum fractions during production of jet fuels. The patents describe exposing petroleum fractions to adsorptive clay structures as a second (or later) processing step for removing contaminants from a potential jet fuel fraction. Examples of suitable adsorbent materials can include various types of natural and/or synthetic clays. The clays can correspond to treated or untreated clays. Examples of clays include attapulgite and/or other types of Fuller's earth. Silica gel can also potentially serve as a suitable adsorbent.